In the usual habitats for this genus, including shores, ditches, mudflats, floodplains, and other moist ground.

Dry specimens are sometimes difficult to distinguish from B. connata, but the species has a distinctive aspect in the field. Bidens comosa is said to have the anthers pale, included in the pale yellow disk corollas, in contrast to blackish anthers in B. connata, exserted beyond the orange disk corollas. The outer phyllaries in B. comosa are large and foliaceous, usually much exceeding the disk; in B. connata they tend to be smaller, fewer, and more linear, but this distinction is poorly defined.

This species and B. connata are sometimes included in the Eurasian B. tripartita L., and sometimes only one or the other of them is so included. The relationships are obviously close, but Michigan plants seem separable.